This grant application outlines plans for studies into the nature of human lactase biosynthesis in health and disease. Under the direction of a successful independent investigator, a three phased approach to this goal will consist of 1) initial investigations using traditional biologic techniques well established in the sponsor's laboratory 2) additional intra- and extramural training in state-of- the-art molecular biology research 3) the eventual application of that training to this specific project. As background for this study, there are animal experiments that support the theory that lactase-phlorizin hydrolase is synthesized as a single chain polypeptide undergoing complex post-translational processing that includes membrane directed N-linked glycosylation and probable intracellular proteolysis to subunit form prior to enzymatic expression at the brush border membrane. Lactase is a unique disaccharidase in regard to the physiologic loss of enzyme activity with weaning in most mammalian species and in respect to the prevalence of clinical deficiency of the enzyme in the adult population. Despite the clinical impact of this rather common disorder, little is known concerning the biosynthesis of the enzyme in human intestine. We propose to examine the synthesis and intracellular processing of human lactase-phlorizin hydrolase using the techniques of pulse-labeling in intestinal organ culture, in vitro cell free translation, and immunoelectron microscopy. We are encouraged that these methods can be applied to this project by our previous success with the techniques in the study of the biosynthesis of sucrase-isomaltase in the rat and in the characterization of normal and abberant processing of sucrase- isomaltase in humans. We hope that the acquisition of additional research skills by the principal investigator will expand the scope of the project to include further investigations incorporating modern molecular techniques. Since we are also in a position to recruit study participants with adult lactase deficiency, we will apply our methods to the detection of an alteration in the normal processing of the molecule that accounts for the loss of enzyme activity in this population. In this fashion, we hope to significantly contribute to the understanding of a common human disease.